v Pneumatic Caulker.—-This, an American invention, was
first introduced in 1890. As shewn in Fig. 302, it was formerly
made by Messrs. Crossley Bros., and would do the work of three
or four men. E is a jacket held in position by the cylinder j,
screwed into the nose-piece F. The caulking chisel G is loose,
but placed within F when required. The piston contains a piston-
valve P, vibrating at right angles to the piston's axis, the slide
hole being closed by slips o o, dovetailed into K. The starting
valve R, when in the position shewn, allows the compressed air,
after entering at L through a strong indiarubber tube, to pass
through the piston by T and u, then harmlessly out by the
passages v and w; but if R be pressed down the passages v w are
closed and the machine operates in the manner to be described.
Key x allows the piston to slide,vertically, but prevents axial
rotation. Y is a passage from T to the piston, and T and u being
formed by flats in s, are not in communication with each other.
There are two passages from the piston to u, seen in plan at z zl9
while in the piston itself one passage j communicates with the top
of the cylinder and another h with the bottom. In addition, two
holes d d^ are made in the slips o o, and grooves e <?b /"/i af e in
connection with these holes at certain times. One other point
must be noticed—the hole g is the exhaust outlet when in
working order, but M fits the hole in the nose-.piece so that air
cannot escape when the piston is at the bottom of its stroke.
If, however, K be lifted to the top position, M will be found just
of a length to disclose an annular space round the curvature N,
and the air is free to pass out at g.
Having noted all the parts, we can now describe the working
of the tool. The workman, after placing the chisel G in the nose-
piece, holds the former with his left hand against the seam of the
boiler as at H, while with his right hand he grasps the boss st
pressing the head R upon it, thus practically closing the passage
u. The air passes through T and Y, but cannot get further.
Hole 4 is now in communication with passage t, however, so the
air enters the valve chamber from the right and moves P to the
left This allows the pressure to act through h on the bottom of
the piston, and the up stroke is made. While this air exhausts at
g, the hole d, being now in communication with f, the valve is